This proposal aims to bring the new field of printed large-area electronics to create flexible, conforming MRI coils printed on clothlike mesh substrates. These flexible coils will fit range of patient sizes and wrap around appendages. Printed arrays can be tailored into garments, improving hospital workflow and easing patient preparation. Thin printed coils, without discrete components, can also potentially be integrated into other systems such as MR-guided high intensity focused ultrasound, MR-PET and X-ray MR. Relevance: MRI receive coil arrays provide increased signal-to-noise-ratio (SNR) over standard single receivers. This excess SNR is often traded for either higher resolution or faster acquisitions. However, a poor fit negates the array's SNR gains. Most coil arrays today have a rigid or semi-rigid structure and are one-size- fits-all, whereas patients come in a variety of sizs and shapes. In fact, it is common to see coil elements offset from the anatomy to the point that the coils have poor fill-factor. This problem is exacerbated in pediatric imaging, and also around adult extremities such as ankles, knees, neck and shoulders. A conformal coil that fits well to convoluted body anatomy can lead to significant SNR gains - as high as 2x or 3x on the surface over standard rigid coils. In addition to SNR gain, ink-printed MRI coils and integrated tuning devices will reduce the number of solder/epoxy connections, improving long-term reliability of flexible coils. Finally, new materials will enable tailored integration of coils in other applicatins such as MR-guided interventions. Approach: Recently, the field of printed electronics has made breakthroughs in fabricating high-precision electronic components directly on a variety of flexible substrates by using ink-based printing techniques. Our plan is to innovate on these processes and fabricate high-sensitivity flexible MRI coils. In Aim 1, we will develop a family of MRI-compatible electronic components for designing resonant receiver coils. Specifically, we will develop non-magnetic printed coil conductors, inductors, capacitors, diodes, and thin-film transistors using conductive, insulating and semiconducting inks. These components will be fabricated onto various mesh-type fabric substrates. We will test, characterize, and validate device performance, both electrically and mechanically. In Aim 2, we will fabricate stand-alone tuned surface coils for 1.5 T and 3 T proton resonance. Based on the results from Aim 1 and Aim 2 efforts, we will design a prototype infant-sized 4-channel coil array in Aim 3. The array wil be tested for mechanical durability, resonant coupling and image quality. Summary: When completed, the proposed research program will provide a unique set of electronic materials for fabricating high-sensitivity flexible coil arrays. As a result, cost-effective custom-designed hardware for improved imaging performance will be available to a broad range of patients. This research will impact emerging applications in wearable medical devices and provide opportunities for integrating thin MRI coils with other imaging modalities.